High-Pressure Synthesis, Crystal Structure, and Magnetic Properties of Mn1-xTxGe4(T:Co, Fe)

Mn1-xTxGe4(T:Co, Fe) solid solution was synthesized at 6 GPa and 650-750°C using a belt-type high-pressure apparatus. The crystal structure of the Mn1-xTxGe4solid solution is related to the β-NiHg4type. The following structural changes were observed in the Mn1-xCoxGe4system: tetragonal (x= 0) to orthorhombic (0 < x< 0.2) and orthorhombic to pseudotetragonal (0.2 ≦ x≦ 0.4). Similar structural changes were also observed at 0 < x< 0.4 (tetra. → ortho.) and x= 0.4 (ortho. → pseudotetra.) in the Mn1-xFexGe4system. These results indicate that the structural changes in Mn1-xTxGe4strongly depend on the average valence electron number of the transition metal atoms. Mn1-xTxGe4solid solutions are itinerant electron ferromagnets and the Curie temperature decreases linearly with decreasing unit-cell volume.